1. Field of the Invention
The present invention relates to a projection-type transmissive image display device having a liquid crystal display panel for producing a display pattern based on light applied to and transmitted through the liquid crystal panel, and more particularly to such a transmissive image display device which includes a planar microlens array for converging light onto each pixel of the liquid crystal panel.
2. Description of the Relevant Art
Some projection-type transmissive image display devices employ a liquid crystal display panel having a matrix of minimum display units known as pixels. The image display devices display desired images and/or characters when independent drive voltages are applied to the pixels to modify optical properties of the liquid crystal of the pixels. Since it is necessary for the pixels to have wires which apply the drive voltages, each of the pixels has a relatively small aperture through which the light passes.
If it is assumed that light applied to liquid crystal display panels has the same intensity, then those crystal display panels which have smaller pixel apertures produce darker images on the screen because the light that is applied to the pixel areas other than the apertures Goes not pass through the apertures.
To solve the above problem, there have been proposed planar microlens arrays comprising circular planar microlenses which are rotationally symmetric with respect to their optical axes and disposed in Confronting relationship to the respective pixels, for converging the applied light onto the pixels (see, for example, Japanese laid-open patent publications Nos. 60-165621, 60-165622, 60-165623, and 60-165624).
As shown in FIG. 9 of the accompanying drawings, one conventional planar microlens array is used with a liquid crystal display panel composed of triads of pixels. The planar microlens array comprises circular microlenses 100 confronting the pixels, respectively. The pixels are spaced horizontally with a pitch a and vertically with a pitch b, the pitches a, b being different from each other. If the difference between the horizontal and vertical pitches a, b is larger, then those areas 101 of the pixels which are not covered by the respective microlenses 100 are larger. Therefore, the light applied to the liquid crystal display panel is not effectively utilized for producing a display pattern, and the image projected onto the screen is relatively dark.
The same problem arises if the horizontal and vertical pitches of pixels are different from each other in other pixel matrix configurations.
As shown in FIG. 5 (a) of the accompanying drawings, a pixel 1b of an active-matrix liquid crystal display panel has an asymmetrically shaped aperture 15 because of an area 16 in which there is located a switching element for applying a voltage to pixel electrodes, such as a TFT (thin-film transistor) or an MIM (metal-insulator-metal) diode.
The circular spot of light converged by each circular microlens 100 is positioned on a line M of the pixel aperture 15, as shown in FIG. 5 (b) of the accompanying drawings. Therefore, an area S of the aperture 15 is remote from the center of the light spot, and is not as effectively used as the other area of the aperture 15. Consequently, the image projected onto the screen is further made darker.